<!DOCTYPE html>
<html lang="zh" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title>我的第一个网页</title>
  </head>
  <body>
    吃了吗,世界!
    <p id="app">hello,world!</p>
    <button type="button" name="button" onclick="f()">点击一下</button>
  </body>
  <script type="text/javascript">
    var x=1;
    function f(){
      document.getElementById('app').innerHTML='点击了'+x++ + '下';
    }
  </script>
</html>
